Ultrasonic Testing And Evaluation Of Creep Damage Based On Nonlinear Longitude Wave Technique

Components and structures being operated at high temperature for long periods usually face the threat of creep damage. Therefore, it is of increasing importance to perform quick and effective testing and quantitative life prediction for structure health monitor (SHM) during creep damage. In this paper, we have performed a research on the characteristics of the nonlinear ultrasonic wave propagating in the creep damaged components or materials after different thermal loadings. The results from this paper may lay a foundation for nondestructive evaluation and life prediction of creep damage by using nonlinear ultrasonic technique.In this research, the creep damaged samples were acquired by high-temperature creep tests based on titanium alloy Ti60 for different holding times, which can represent the simulation of various creep damage levels. Then, the microstructure changes of the creep degraded samples were observed based on metallographic studies, such as scanning electron microscope (SEM) and optical microscope (OM). The ultrasonic parameters such as velocity, attenuation coefficient, second harmonic based nonlinear parameter and third harmonic based nonlinear parameter of these samples are measured using the SNAP 5000 high power ultrasonic testing system. The results show that:(1) The longitudinal velocity does not change significantly during the creep process. (2) The attenuation coefficient does not change significantly during the early creep period, but it increases obviously in the latter period. (3) The second harmonic based nonlinear parameterβis sensitive to the creep damage, whose variation reaches to 80% compared with that of the initial state. Moreover, the change ofβdoes not exhibit a monotonic increase with increasing creep life, but an oscillatory increase.Finally, we proposed a nondestructive evaluation method based on the nonlinear parameterβfor life prediction of metallic material under creep loading.